This invention relates to magnetically controlling catheters, and in particular to a method and apparatus for magnetically controlling catheters in body lumens and cavities.
It has long been proposed to navigate a magnet-tipped catheter through the body with an externally applied magnetic field. See for example Yodh, A New Magnet System for Intravascular Navigation, Medical and Biological Engineering, Vol. 6, No. 2, March 1968. However, until this invention, the methods of navigating have been too crude and unreliable for serious medical applications. Thus, at the present time the guidance of catheters and other medical devices in body lumens and cavities is still most often accomplished by providing a bent tip on the device or using a guide wire with a bent tip. The physician applies torque and axial push force on the proximal end of the medical device or guidewire to effect tip direction and axial advancement at the distal end. This method of orienting and advancing the tip has several limitations. First, the torque and axial push force is randomly distributed to the distal tip due to the length of the catheter and the tortuousness of the path. Second, the alignment of the catheter in the required direction needs to be synchronized with the advancement of the catheter without changing the catheter orientation. With these two complications, it becomes very difficult to control the distal tip of the catheter from the proximal end. Another method of navigating medical devices through the body is to use blood flow in blood vessels to guide the device through the blood vessels. Although these navigation techniques are effective, they are tedious, require extraordinary skill, and result in long medical procedures that fatigue the user.
The method and apparatus of the present invention facilitate the navigation of a magnet-tipped medical device through body lumens and cavities. Generally, the method of the present invention comprises: inputting information about the desired path of the medical device; determining the appropriate magnetic field direction and intensity to orient the distal end of the medical device in the direction of the desired path, and applying a magnetic field to the distal end of the medical device to orient the distal end in the direction of desired path. In accordance with this invention, path information is input by providing bi-planar displays of the portion of the body through which the medical device is being navigated. The desired path, and more particularly points along the desired path, is identified on each of the displays. In accordance with a first embodiment of this invention, the user identifies the point where the user desires a direction change (which is usually where the catheter tip is positioned) and a point on the desired new path on each of the displays. The identification of the points on the two bi-planar displays uniquely identifies the points in the three dimensional space inside the body part. The direction of the line or vector including the two points is then determined, and the magnet system is operated to create a magnetic field in the direction of this vector, to orient the distal tip of the catheter.
In accordance with a second embodiment of this invention, the user identifies three points on the two bi-planar displays: a point on the current path of the catheter, the point where the user desires to initiate a direction change, and a point on the desired new path of the catheter. The identification of the points on the two bi-planar displays uniquely identifies the points in the three dimensional space inside the body part. The desired angle of deflection is then determined, and the magnet system is controlled to apply a magnetic field in a direction that provides the maximum over torque (i.e., leads the desired angle of deflection by 90xc2x0 in the same plane as the desired angle of deflection). The intensity of the magnetic field is determined based upon a table of empirical data which characterizes the required magnetic field strength for a given angle of deflection for a particular medical device.
Generally, the apparatus of the present invention comprises a magnet system for applying a magnetic field to the magnet-tipped distal end of a medical device, to navigate, orient, and hold the distal end of the medical device in the body. The apparatus also includes a computer for controlling the magnet system. First and second imaging devices, connected to the computer, provide images of the body part through which the catheter is being navigated. The computer displays these images on two displays. A controller, connected to the computer, has a joystick and trigger for the user to input points on the displays for two-point and three-point navigation according to the principles of the present invention.
The method and apparatus of the present invention are particularly adapted for use with an elongated medical device such as a catheter, but could be used with a guidewire or other device. In the preferred embodiment, the catheter consists of a distal section that contains a permanent or permeable magnet with an inner hole to allow the passage of fluids and other agents.
The method and apparatus of this invention allow for fast and efficient navigation of magnetic tipped catheters and other medical devices in the body. The method and apparatus provide an easy to use, intuitive interface that allows the user to identify the desired path on an image of the body. The angle of change and the necessary magnetic field to effect that change are automatically determined. The determination of the necessary magnetic field automatically accounts for the lag angle and other physical properties of the catheter. A limit on the angle of deflection can also be imposed to reduce the time necessary for the magnet system to operate, thereby speeding the navigation through the body. These and other features and advantages will be in part apparent, and in part pointed out hereinafter.